[ntp:questions] NTP not syncing
Brian.Inglis at SystematicSw.ab.ca
Fri Dec 6 13:00:41 UTC 2013
It would be better if ntpd used the drift file frequency for the first
two hours, instead of 15 minutes, before coming up with its (currently
wild assed) guesstimate, and then spending 4 hours getting back to the
This is on Windows 7, current stable ntpd, NMEA user mode pps ref clock
(serialpps does not work with a 64 bit PCIe serial port driver stack).
I try to avoid any issues by copying the drift file daily, if it is
within limits, and copying back before startup, if it outside limits,
to reduce issues with wild ntpd drift estimates.
Could whatever was patched in Linux be required in the Windows port?
Take care. Thanks, Brian Inglis
On 2013-12-06 03:27, Charles Elliott wrote:
> You might be able to do better. In QC an average of a randomly gathered
> sample of a continuous variable is distributed as normal (Gaussian).
> If NTPD kept a few more statistics (state), it could measure the freq
> and determine if it is outside of 3 standard deviations of the grand
> mean of past observations of freq. If it is outside then gather several
> more observations of freq (5 total would be best, but 2 or three might
> do) and compute the average. If that average is outside 3 stdDev of
> the mean, then the probability of that result is so low (< 0.05) that
> it could not have happened by chance; something has changed. NTPD must
> use the new average as the current freq and include it in the grand mean,
> but the user should be warned that something is awry. On the other hand,
> if the 2 or 3 new observations of the freq are not close to the original,
> then just throw away the latter.
> Charles Elliott
> -----Original Message-----
> From: questions-bounces+elliott.ch=verizon.net at lists.ntp.org
> [mailto:questions-bounces+elliott.ch=verizon.net at lists.ntp.org] On Behalf Of
> Sent: Friday, December 6, 2013 3:47 AM
> To: questions at lists.ntp.org
> Subject: Re: [ntp:questions] NTP not syncing
> On 2013-12-06, David Taylor <david-taylor at blueyonder.co.uk.invalid> wrote:
>> On 04/12/2013 21:25, Terje Mathisen wrote:
>>> It is very common, IF you are running on Linux!
>>> The base frequency is recalculated each time you restart, which means
>>> that steps of 100-200 ppm from one reboot to the next can be expected.
>> I'm surprised to hear of this problem, as I've not been aware of it in
>> years of running FreeBSD systems, and in more than a year of running
>> (now) five Raspberry Pi Linux systems. Perhaps I've been lucky? As
>> they are mainly experimental PCs, the RPi cards are rebooted more than
> As I said, I think that in the more recent kernels Linux has fixed this.
> Since the RPi is only about 2 years old, its linux is a recent kernel.
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